High speed centrifuge drive assembly

ABSTRACT

A drive assembly for a motor driven centrifuge, or other rotatable mechanisms, is provided which includes a resilient rotatably driven spindle. The rotating spindle and centrifuge rotor normally create gyroscopic effects so that the rotor is rotated with minimal radial vibration about a mass center, even in the presence of some unbalancing of the rotor assembly. The apparatus also includes contact means associated with the spindle for providing a desired electrical control signal should the rotor unbalancing exceed a safe threshold. The control signal is used normally to de-energize the drive motor and to cause the rotor to stop.

United States Patent Drucker 1 July 11, 1972 541 HIGH SPEED CENTRIFUGEDRIVE 770,385 9/1904 Pott ct al .233/23 A ASSEMBLY 1,824,722 9/1931Jones ........233/23 2,431,316 11/1947 Dudley et a1... .....3l0/68 B 21lnvemon Kenneth s- 3,226,016 12/1965 Coupel61a1........................233/23 A onsu th f. [73] Assignee Bio-CRants, Inc Sol-l Gate Call Primary xaminer D F- w Filed: MINI 2, 1970Assistant Examiner-B. A. Reynolds [2n APPL No: 15,761 Anorney.lessup&Beecher ABSIRACT [s2] ga wslz ig gd A drive assembly for a motor drivencentrifuge, or other 5| 1 Int Cl 6 "/00 rotatable mechanisms, isprovided which includes a resilient [s8] 3 66 91 rotatably drivenspindle. The rotating spindle and centrifuge 310/157, 5 l 68 5;IBIS/460, 462, 466, 489, I28; 233/23, 23 A; 64/] l; 200/79, 6|.4S,6!.46, 6|.S2

rotor normally create gyroscopic eflects so that the rotor is rotatedwith minimal radial vibration about a mass center, even in the presenceof some unbalancing of the rotor as sembly. The apparatus also includescontact means associated CM with the spindle for providing a desiredelectrical control UNlTED STATES PATENTS signal should the rotorunbalancing exceed a safe threshold. The control signal is used normallyto de-energize the drive 2,827,229 3/1958 Blum .233/23 motor and tocause the to stop 3,322,338 5/1967 Stallman et al.. ...233/23 2,725,188I l/l955 Scott ..233l23 9 Claims, 4 Drawing Figures lfli P'A'TENTEDJUL n2912 3. 676. 723 sum 1 or 2 Ma gg/a/ w xrrai/var f HIGH SPEEDCEN'I'RIFUGE DRIVE ASSEMBLY BACKGROUND OF THE INVENTION As mentioned,for example, in U.S. Pat. No. 2,827,229, a critical problem in theconstruction of electric motor driven centrifuges lies in providing forsafely balancing the rotating rotor head of the centrifuge. For example,in the prior art structures, the rotor of the centrifuge including therotating head, must be concentrically balanced within severe tolerancesso that the rotational axis of the rotor may closely coincide with itsgeometrical axis. When the prior art rigid couplings are used in therotor drive construction, the slightest departure from ideal rotorbalance produces substantial stress and strain on the bearings and driveshaft of the apparatus when the rotor assembly is driven at relativelyhigh speed.

As also pointed out in the aforesaid United States patent, it is a wellknown fact that a rotating, rigid body, if freely suspended, tries torotate about an axis through the center of gravity of the body. Thus, ifa perfectly machined and dynamically balanced rotor were spun about itsaxis, a smooth running condition without vibration is theoreticallyobtainable. If, however, a weight is added to a certain portion of therotor, the center of gravity of the overall assembly is displacedlaterally from the geometrical axis, and as a result the rotor now spinsabout a new axis passing through a new center of gravity.

In the prior art assemblies, even if the rotor is unbalanced only to asmall degree, violent vibrations will be produced not only in the rotor,but also in its mounting and in the drive motor as well, as the rotorcomes up to speed. If the prior art apparatus is permitted to continueoperating under such a condition for any length of time, the mountingswill be destroyed, and there also is a possibility of the apparatusthrowing itself to pieces and thereby endangering the safety of anyonein the vicinity and damaging the surrounding property.

In an attempt to reduce such rotor vibrations, a compound flexiblecoupling system is provided in the mechanism described in the aforesaidpatent for coupling for the rotor and for the rotor drive shaft. This isso that the drive shaft may perform as an articulating drive between anunbalanced rotor and a stationary motor base assembly, therebypermitting the geometric axis of the rotor to describe its naturaldynamic axis in an orbital path.

A like effect is provided in the mechanism of the present invention bythe provision of a resilient spindle in the drive assembly. Then, in thepresence of slight unbalances in the rotating motor, the resilientspindle assumes an S shape. This is because the gyroscopic effect causesthe rotor to spin about an axis passing through the center of gravity ofthe rotor, and this spinning is accomplished with minimal vibration.Should the rotor unbalance become too pronounced in the mechanism of theinvention, an electric contact is established from which a control maybe derived for quickly de-energizing the drive motor and causing therotor to come to a halt.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side sectional view of ahigh speed motor driven centrifuge which may incorporate the conceptsand teachings of the present invention;

FIG. 2 is a side sectional view of a portion of the mechanism of FIG. Iand constructed in accordance with one embodiment of the invention;

FIG. 3 is a view like FIG. 2, and representing a slightly modifiedembodiment with respect to the mechanism of FIG. 2; and

FIG. 4 is a circuit diagram of a suitable electrical control system foruse in conjunction with the mechanisms of FIGS. 2 and 3.

DETAILED DESCRIPTION OF THE. ILLUSTRATED EMBODIMENTS As shown in FIG. I,for example, the centrifuge assembly may include a cabinet l which alsoserves as a frame for supporting the various components of the assembly.As illustrawd, the cabinet may conveniently be supported on wheels, suchas the wheels I2. A housing 14 is supported within the cabinet I0, andthe housing 14 provides an inner compartment for the apparatus. Thehousing I4 may, for example, be welded to the upper rim of the cabinetI0.

An access lid I6 may be lu'nged over the top of the housing 14, asshown. The lid 16 is hinged by an appropriate hinge I8, and it may belatched in place by an appropriate latch mechanism 20. An annular seal22 is provided around the upper rim of the assembly so that the lid istightly sealed in place when it is closed and latched. An appropriateair filter 24 may be provided on the lid 16. A control panel 26 ismounted on one side of the cabinet I0, and usual controls, includingspeed and timer controls are mounted on the control panel 26.

The bottom of the housing 14 may provide an appropriate mounting framefor an electric motor 30 and drive assembly 32. The drive assembly 32will be described in some detail subsequently, and it serves to couplethe electric motor 30 to the centrifuge head 34. As shown, the motor issuspended from the lower side of the housing I4 on hanger brackets 36,and is secured to the brackets by fasteners 38 which extend throughappropriate rubber bushing vibration dampeners 40.

It will become apparent in the description proceeds that the structureshown in FIG. I represents but one appropriate type of apparatus inwhich the drive assembly of the present invention may be incorporated,and that the drive may be included in any apparatus in which a rotor isto be rotatably driven.

As shown, for example, in FIG. 2, the drive assembly 32 includes anelongated resilient spindle I02 composed, for example, of an appropriatealloy such as UNIMAR" or any other appropriate material exhibiting highstrength and good resiliency characteristia may be used. The upper endof the drive shaft 106 from the motor 30 may be tubular, as shown, andthe lower end of the spindle I02 may extend down into the motor driveshaft to be secured thereto by means, for example, of set screws 108.The lower end of the spindle I02 may have a rectangular configuration,as may the inner bore of the drive shah I06, and the lower end of thespindle may be enlarged with respect to the remaining part of thespindle, as shown.

The spindle I02 extends vertically upwardly from the motor, and throughthe tubular bushing 100. A tubular drive shaft 110 is mounted on theupper end of the spindle I02, and the drive shaft 110 extends along thespindle, as shown, in coaxial relationship with the spindle and spacedradially therefrom. The upper end of the tubular shaft I10 has a taperedthread, and a nut 112 is threaded down over the tubular shaft 110, so asto bring the upper end of the tubular shaft 110 into a pressfit with theenlarged upper extremity of the spindle 102.

The tubular shalt I I0 is rotatably supported in bearings which, inturn, are mounted to the tubular bushing 100. The bearings 120 may be,for example, New Departure bearings, or any other suitable type. Thebearings I20 include a tubular retainer 126 which has a pair ofshoulders 126a and I26! formed on the outer peripheral surface andspaced axially from one another, as shown.

A flexible seal 130 is attached to the upper shoulder I26 and is held onthe upper end of the bushing 100 by means of a band I32. The seal I30serves as a dampener for the bearing, and it also serves to seal theinterior of the housing I4 from hot air which emanates, for example, inthe motor 30. The seal 130 also serves to prevent any chemicals whichmight be spilled in the housing 14 from injuring the interior of thebushing or into the motor assembly. The lower annular shoulder 12Gbsupports an annular rubber bumper I36. Appropriate 0- rings [38 areprovided in the bearing assembly, as shown. Split retainer rings I40serve to retain the bearings within the tubular retainer 126.

A shoulder I42 is threaded onto the tubular shah 1 10 directly over thebearing assembly. This latter shoulder serves as a support for thecentrifuge head 34. The head 34 and a tapered collet 146 are held on theshoulder 142 by means of a locking nut 150 which is threaded to thecollet. An annular member 152 may be threaded into the upper end of thelocking nut 150. The annular member may be used to support a lid for theassembly. A plug 154 may be threaded into the end of the tubular shaft110, and over the upper extremity of the spindle 102. The shoulder 142also acts as a slinger to prevent liquids from entering the bearings120.

A feature of the structure shown in FIG. 2 is that the spindle 102 maybe removed therefrom without disturbing the entire assembly. This may beachieved, for example, by loosening the set screws 108 at the lower endof the spindle; and by removing the annular member 152 and the plug 154,and by loosening the nut H2 at the upper end of the spindle. The spindle102 may then be withdrawn from the tubular shaft 110.

The embodiment of FIG. 3 is generally similar to the embodiment of FIG.I, and like componenm have been designated by the same numbers. Theslinger shoulder M2 in the assembly of FIG. 3 is generally similar tothe shoulder 142 of the previous embodiment except that the shoulder142' is in press-fit with the tubular shaft I10. In the embodiment ofFIG. 3, the spindle 102 is attached at its upper end to the tubularshaft 110' by, for example, silver soldering, rather than by thearrangement described in conjunction with FIG. 2. In the latterembodiment, the rotor may be supported on the shoulder 142 by a fastenerextending into the threaded upper extremity of the tubular shaft 110'.

The motor drive shaft 106 is supported in a bearing 200 which, in turn,is mounted on the motor frame 202. A tubular member 204 is supported onthe motor frame in coaxial relationship with the spindle 102, butinsulated from the motor frame and spindle by an insulated washer 206.The tubular member 204 may be made of brass or other appropriateelectrical conductor.

An electric contact is made to the tubular member 204 by means, forexample, ofan electric lead 210 and contact screw 212. The tubularmember is supported on the insulated washer 206 by means of a collar 220and spring loaded screws 222. The screws may be formed of nylon, orother suitable insulating material.

Should the head of the centrifuge be loaded in a manner to unbalance therotor in excess of a safe threshold, the resulting vibration causes thelower end of the tubular shaft to contact and effectively ground" thetubular member 204. The lead 210 may be connected to an appropriatecontrol circuit such as shown in FIG. 4, so that any such groundingofthe tubular member 204 causes the motor 30 to be de-energized and therotor brought to a stop.

The control circuit of HO. 4 includes, for example, a transformer 300which has a secondary winding connected to the lead 210 and to thegrounded casing of the motor 30. The primary winding of the transformer300 is connected to one terminal of a suitable power source, and throughthe winding of a relay 302 to the other terminal of the power source. Areset switch 304 may also be included in the latter connection. Oneterminal of the power source is connected to the motor 30, and the otherterminal is connected to a pair of normally closed contacts of the relay302 to the other terminal of the motor. The relay 302 also includes apair of normally open latching contacts which, when closed, cause therelay to be held closed by the closure of its normally open latchingcontact.

During normal operation of the system, the relay 302 is deenergized, andthe motor 30 is energized through the normally closed contacts of therelay 302. However, when the condi tions are such that the sleeve 204 isgrounded, in the manner described above, the secondary winding of thetransformer 300 is short-circuited, so that an increased current flowsthrough the primary winding. This increased current energized the relay302 causing its normally closed contacts to open, so that the motor 30is de-energized. At the same time,

the latching contacts of the relay 302 close, so that the relay remainsenergized, and the motor 30 remains de-energized,

until the reset switch 304 is actuated.

lt W111 be appreciated that other types of control circuits may be usedto achieve the desired de-energizing of the motor 30. Also, other relaycontacts may be incorporated into the relay 302, so as to activate alarmcircuits, energize braking mechanisms for the motor 30, and so on.

It will be appreciated that although particular embodiments of theinvention have been shown and described, modifications may be made. Allmodifications which come within the spirit and scope of the inventionare intended to be covered by the following claims.

What is claimed is:

l. A rotatable rotor assembly comprising a frame; a motor mounted onsaid frame; a resilient spindle mechanically coupled to said motor andextending vertically upwardly therefrom to be rotatably driven thereby;a rotor; means for mounting said rotor on said spindle at the upper endthereof remote from said motor to be rotatably driven by said spindle; atubular electrically conductive member mounted in fixed relationshipwith said frame and insulated therefrom, said tubular member extendingupwardly along said spindle in coaxial relationship therewith but spacedradially therefrom; and electrical contact means mounted on the upperend of said spindle for engagement with said electrically conductivemember when the radial deflection of said spindle exceeds a particularthreshold.

2. The asembly defined in claim 1, and which includes a tubular driveshaft mounted on the upper end of said spindle and extending downwardlyalong said spindle in coaxial relationship therewith; a tubular bushingmounted on said frame and surrounding said spindle; bearing means forsaid spindle; and flexible sealing means mounting said bearing means tosaid bushing.

3. The assembly defined in claim 2, and which includes an annularshoulder member mounted on said tubular drive shaft above said sealingmeans and adjacent thereto for protecting said bearing means fromliquids and serving as a support for said rotor.

4. The assembly defined in claim 2, in which said tubular drive shafthas a tapered thread at the upper extremity thereof, and which includesnut means engaging said tapered thread to produce a press-fit betweenthe upper extremity of said tubular shah and the upper extremity of saidspindle.

5. The assembly defined in claim 2, in which said tubular drive shaft isattached at the upper extremity thereof to the upper extremity of saidspindle.

6. The assembly defined in claim 2, in which said bearing means includesa tubular retainer having an annular shoulder thereon; and a resilientannular bumper member mounted on said annular shoulder.

'7. The assembly defined in claim 2, in which said tubular electricallyconductive member is positioned to be engaged by the lower end of saidtubular drive shaft when the radial deflection of said spindle exceeds aparticular threshold.

8. The assembly defined in claim I, in which includes an electriccontrol circuit connected to said tubular member and to said motor forde-energizing said motor upon the engagement of said electrical contactmeans with said electrically conductive tubular member.

9. The assembly defined in claim 8, in which said control circuitincludes a transformer having a secondary winding connected across saidtubular member and said electrical contact means to be short-circuitedwhen said electrical contact means engages said tubular member, andwhich includes a latching relay circuit connected to the primary of saidtransformer for deenergizing said motor when said secondary winding isshort-circuited, and for maintaining said motor de-energized until thecontrol circuit is reset.

1. A rotatable rotor assembly comprising a frame; a motor mounted onsaid frame; a resilient spindle mechanically coupled to said motor andextending vertically upwardly therefrom to be rotatably driven thereby;a rotor; means for mounting said rotor on said spindle at the upper endthereof remote from said motor to be rotatably driven by said spindle; atubular electrically conductive member mounted in fixed relationshipwith said frame and insulated therefrom, said tubular member extendingupwardly along said spindle in coaxial relationship therewith but spacedradially therefrom; and electrical contact means mounted on the upperend of said spindle for engagement with said electrically conductivemember when the radial deflection of said spindle exceeds a particularthreshold.
 2. The assembly defined in claim 1, and which includes atubular drive shaft mounted on the upper end of said spindle andextending downwardly along said spindle in coaxial relationshiptherewith; a tubular bushing mounted on said frame and surrounding saidspindle; bearing means for said spindle; and flexible sealing meansmounting said bearing means to said bushing.
 3. The assembly defined inclaim 2, and which includes an annular shoulder member mounted on saidtubular drive shaft above said sealing means and adjacent thereto forprotecting said bearing means from liquids and serving as a support forsaid rotor.
 4. The assembly defined in claim 2, in which said tubulardrive shaft has a tapered thread at the upper extremity thereof, andwhich includes nut means engaging said tapered thread to produce apress-fit between the upper extremity of said tubular shaft and theupper extremity of said spindle.
 5. The assembly defined in claim 2, inwhich said tubular drive shaft is attached at the upper extremitythereof to the upper extremity of said spindle.
 6. The assembly definedin claim 2, in which said bearing means includes a tubular retainerhaving an annular shoulder thereon; and a resilient annular bumpermember mounted on said annular shoulder.
 7. The assembly defined inclaim 2, in which said tubular electrically conductive member ispositioned to be engaged by the lower end of said tubular drive shaftwhen the radial deflection of said spindle exceeds a particularthreshold.
 8. The assembly defined in claim 1, in which includes anelectric control circuit connected to said tubular member and to saidmotor for de-energizing said motor upon the engagement of saidelectrical contact means with said electrically conductive tubularmember.
 9. The assembly defined in claim 8, in which said controlcircuit includes a transformer having a secondary winding connectedacross said tubular member and said electrical contact means to beshort-circuited when said electrical contact means engages said tubularmember, and which includes a latching relay circuit connected to theprimary of said transformer for deenergizing said motor when saidsecondary winding is short-circuited, and for maintaining said motorde-energized until the control circuit is reset.